ACEIZE

From Planet Pride on Myspace, via ESA.


This is an artist's impression of a Jupiter-sized planet passing in front of its parent star. Such events are called transits. When the planet transits the star, the star’s apparent brightness drops by a few percent for a short period. Through this technique, astronomers can search for planets across the galaxy by measuring periodic changes in a star’s luminosity.



The first class of exoplanets found by this technique are the so-called “hot Jupiters,” which are so close to their stars they complete an orbit within days, or even hours.



Credits: NASA, ESA and G. Bacon



COROT has provided its first image of a giant planet orbiting another star and the first bit of ‘seismic’ information on a far away, Sun-like star, with unexpected accuracy.



The unanticipated level of accuracy of this raw data shows that COROT will be able to see rocky planets -- perhaps even as small as Earth - and possibly provide an indication of their chemical composition. COROT, a CNES project with ESA participation, is a mission with a dual goal. It is the first space mission dedicated entirely to the search of extra-solar planets. It provides a wide-field survey of planets like our own at an unprecedented level of accuracy. It is also making the most comprehensive study ever of the interior of stars other than our Sun. Both objectives are achieved by analysing the behaviour of light emitted by a target star.



An exoplanet is detected by COROT due to a sudden decrease in the intensity of light or the ‘light curve’ of a parent star when a planet transits in front of it.

This image shows the signature of the presence of a planet orbiting a star. The intensity of light coming from the star is represented on the y-axis whereas the x-axis shows the phase, or the revolution of the planet around the star.



The amount of light from the star reaching COROT decreases each time the planet passes in front of the star itself. This is when the drop is registered.



This was the first planet detected by COROT since the beginning of its mission. This light curve is part of a data set obtained between February and April 2007.



The planet is a very hot gas giant, of radius equal to 1.78 times that of Jupiter. The planet takes 1.5 days to revolve around the star.



Coordinated spectroscopic observations from the ground have allowed to determine that the mass of the planet is about 1.3 times that of Jupiter. The parent star is a yellow dwarf star similar to our Sun. It is located in the direction of the constellation Unicorn (Monocerus), roughly 1,500 light years from us.

Credits: COROT exo-team



The study of stellar interiors – or ‘asteroseismology’ – is carried out by analysing the oscillations in the light curve of the star. The oscillations are created due to mechanical waves propagating in the star itself and they give a clue to the structure of its interior.



COROT’s strength lies in the continued observation of the same targets in a given area of the sky. The observations have been on since the science operations began, 60 days ago. Another strong point is the accuracy with which it measures the variations in the luminosity of the star.



The first planet detected by COROT, now named ‘COROT-Exo-1b,’ is a very hot gas giant, with a radius equal to 1.78 times that of Jupiter. It orbits a yellow dwarf star similar to our Sun with a period of about 1.5 days. ‘COROT-Exo-1b’ is situated roughly 1500 light years from us, in the direction of the constellation Unicorn (Monoceros). Coordinated spectroscopic observations from the ground have also allowed the determination of the mass of the planet, equivalent to about 1.3 Jupiter masses.



The scientific evaluation of the results that are streaming in will take some time. “The data we are presenting today is still raw but exceptional,” says Malcolm Fridlund, COROT Project Scientist for ESA. “It shows that the on-board systems are working better than expected in some cases -- up to ten times the expectation before launch. This will have an enormous impact on the results of the mission.”

As the planet passes in front of its parent star, the brightness of the star decreases. Figure based on image by Hans Deeg, from ' Transits of extrasolar planets'.



Credits: Hans Deeg



All the sources of noise and disturbance have not yet been taken into account in the data. This first exoplanet was detected with an error of only 0.0003 or 0.03% during one hour of observation.



On applying all the corrections to the light curves, the error will be reduced to only 5 parts out of 100,000. When many transits of the planet in front of the star are observed, the precision will approach just one or a few parts out of 100,000.

As a consequence, small planets down to the size of our Earth – three times smaller than initially thought possible -- will be in the grasp of COROT. The satellite may also be able, in specific circumstances, to detect subtle variations in the stellar light reflected by the planet itself. This would give an indication of its chemical composition.



The quality of the asteroseismological data is equally impressive. Excellent ‘starquake’ data were obtained during the first 60 days of observations, with a margin of error of less than one part per million.







This image shows the light curve emitted by a binary star system as seen by COROT. The crests show light emitted by both stars. However, when one star eclipses the other, the troughs are created due to a decrease in the amount of light reaching COROT. The periodicity is seen since the stars are revolving around each other with a fixed period.



The light curve was obtained by COROT during observations performed between February and April 2007.



This high quality of this light curve is due to the continuity of the observations and their high accuracy.

Credits: COROT exo-team



COROT observed a bright Sun-like star continuously for 50 days, showing large, unexpected luminosity variations on time scales of a few days. This may be related to the star’s magnetic activity.



The accuracy of these measurements was truly outstanding: with an error of five parts out of 100,000 in one minute (corresponding to one part per million over four minutes), COROT has already reached the maximum performance for a telescope of its size.



The preliminary analysis of the oscillations in stellar luminosity clearly shows the seismic signature typical of a Sun-like star. This analysis will eventually help scientists understand the star’s internal structure and age.



“COROT, a joint endeavour between France, Europe and Brazil under the leadership of CNES, was certainly born under a lucky star,” concluded Fridlund. “After a perfect launch, and a faster-than-expected start of its science operations, we have been eagerly awaiting its data. Now, having seen its quality, we can expect great discoveries in the future.”



Notes for editors

COROT was launched by a Soyuz rocket from the Baikonur cosmodrome in Kazakhstan on 27 December 2006. Settled in its almost-circular polar orbit ranging between 895 and 906 kilometres above the Earth's surface, the spacecraft was powered on on 2 January 2007 and started its science observations on 3 February this year.



COROT is a CNES project with ESA participation. The other major partners in this mission are Austria, Belgium, Brazil, Germany and Spain.



For more information:



Malcolm Fridlund, ESA COROT Project Scientist

Email: Malcolm.Fridlund @ esa.int

from: ESA Science & Technology



Unexpected Quality of Raw Data from Early COROT Observations



03 May 2007



CoRoT started its first science observation period on 3 February 2007 and has already returned data with a quality that is exceeding the pre-launch expectations. CoRoT's accurate and continuous observations of stellar luminosities for selected stars allows for the study of their interiors and for the detection of exoplanets when they transit their parent star.



The data presented here are raw and not yet fully calibrated, but already reveal the above-expectation capabilities of the spacecraft instruments. Image 1 shows the transit of the first exoplanet discovered by CoRoT, CoRoT-Exo-1b, a Jupiter-sized planet orbiting a solar type star in the direction of the Monoceros constellation. The accuracy in measuring the parent star's brightness in this raw data is already 5 × 10-5 per minute and once processed will be 10-6 per minute.

Date: 03 May 2007

Satellite: CoRoT

Depicts: Transit of exoplanet CoRoT-Exo-1b

Copyright: CoRoT exo-team



This plot shows the transit of the first exoplanet discovered by CoRoT: CoRoT-Exo-1b. The planet's transit results in a decrease in the luminosity of the hosting star when the planet passes in front of it, which is observed by CoRoT. The parent star is a Sun-like star.



CoRoT-Exo-1b is a very hot giant planet, similar to Jupiter and with a radius preliminary estimated between 1.5 and 1.8 times Jupiter's radius (given CoRoT's excellent phometric data, most of the uncertainty is in fact due to the uncertainty on the radius of the parent star, which is still preliminary).

Thanks to combined spectroscopic observations from the ground, the mass of the planet has also been derived and found to be around 1.3 times that of Jupiter. CoRoT-Exo-1b is orbiting its parent star in 1.5 days.



This first exoplanet was detected with an error of only 5 × 10-5 during one hour of observation. When all the corrections are applied to the light-curves, the error will be reduced to only 10-5.







Date: 03 May 2007

Satellite: CoRoT

Depicts: Light curve of an eclipsing binary

Copyright: CoRoT exo-team

Light curve of an eclipsing binary of magnitude 13, showing the reflected light between the two components. This figure illustrates both the continuity of the CoRoT observations during a longer period of time, and the achieved accuracy of the flux measurements which is better than 10-3 in 8 minutes of integration time.



Variations in the light of another bright solar type star, that was observed continuously during a ~50 day period, show fluctuations on time scales of a few days (image 3). The accuracy of the raw data again is 5 × 10-5 per minute. Spectral analysis of the corresponding frequency power spectrum (image 4) will allow study of the star's internal structure and its age.







Date: 03 May 2007

Satellite: CoRoT

Depicts: Plot of relative light variations

Copyright: CoRoT asteroseismological team

Relative light variations of a bright solar type star observed continuously during a 50 day period showing quite large unexpected variations on time scales of a few days, possibly related to magnetic activity.



The accuracy of the measurements is 5 × 10-5 per minute, which corresponds to the ultimate accuracy that can be achieved for the CoRoT telescope at the required integration times due to the quantum nature of light (which introduces Poisson noise that becomes a limiting factor for the brightest stars)







Date: 03 May 2007

Satellite: CoRoT

Depicts: Light variation power spectrum for frequencies 1.5 - 2 mHz

Copyright: CoRoT asteroseismological team

This plot shows the power spectrum in arbitrary units (P) as a function of frequency (f), for the light curve of a solar type star (see related images). The spectral analysis of the light curve, reveals small periodic components in the expected domain from 1.5 to 2 mHz. These periods, corresponding to modes of oscillation of the star will be studied and interpreted to understand the star's internal structure and determine its age.